Typically in such a machine where the gas flow into the expander may be in excess of 200 liters per minute, a lubricant must be supplied and injected into the expansion chamber of the machine, at a rate of around 10 milliliters per minute. In addition to the cost of using mineral oil lubricants at such a flow rate and accommodating a reservoir of sufficient size, there are additionally difficulties in subsequently separating the lubricant from the gas exhausted from the expander, since the lubricant will typically be entrained as a mist or fume.